Over the last few years, optical fibers are being widely used for communications. The present day coherent communication systems use the dense wavelength division multiplexing techniques to transfer the data. Several coherent modulation techniques such as OOK or QPSK with single mode fibers have been used to increase the data rate capacity of the communication system by taking almost all the freedoms available in modulation schemes. The telecommunication industry is continuously striving for the designs to meet the exponential increase in the data rate capacity demand. The ongoing research suggests that the few mode fiber which can allow the light to travel more than one mode with spatial division multiplexing schemes can be a potential solution to increase the data rate by allowing the signal to transmit in more than one mode. Typically, the performance of these optical fibers is determined based on dispersion, intermodal crosstalk occurring due to spatial overlap between guiding modes and bending losses over a broad range of wavelength. In general, the dispersion, spatial overlap and bending losses are optimized based on a refractive index profile. The refractive index profile defines the properties of a core section and a cladding section. Also, the refractive index profile illustrates a relationship between the refractive index of the optical fiber with a radius of the optical fiber. Further, this profile is determined based on a concentration of dopants and materials used during manufacturing. Furthermore, the dispersion, spatial overlap between modes and bending losses are controlled by varying the thickness of each region of the optical fiber.
Currently available profiles of few mode fibers are not optimized for dispersion and spatial overlap between the Lp01 mode and Lp11 mode to use in broad band SDM applications in S, C and L bands. This results in intermodal crosstalk between the guiding modes. In prior art U.S. Pat. No. 8,971,682 B2, a few mode optical fiber is disclosed which can be operated in two or more modes. The prior art provides a trench region after the central core and high index ring in the few mode optical fiber. However, the prior art does not optimize the dispersion properties and spatial mode overlap which in turn reduces the intermodal crosstalk. Low dispersion is necessary to use few mode optical fibers in space division multiplexing applications in the wavelength range from 1460 nm to 1625 nm.
In light of the above stated discussion, there is a dire need for a few mode optical fiber with dispersion control and minimized spatial overlap for low intermodal crosstalk between the modes while being suitable for SDM systems in long haul communications.